This invention relates to a measuring device with the capability of automatically exchanging samples, comprising an automatic sample changer on which a plurality of samples can be selectably set and a main body which contains a control unit for controlling the operation of this automatic sample changer for selecting a sample. Such a measuring device can be utilized in a spectrometer using an automatic sample changer having a plurality of samples set along the outer periphery of a rotatable circular disk.
When it is desired to measure a plurality of samples continuously, one frequently uses an accessory device such as an automatic sample changer or an automatic sampler adapted to automatically select or exchange a plurality of samples and transport them to a specified position for the measurement. With the help of such an accessory device, the user can set up all the desired samples prior to the beginning of the measurements and need not necessarily be present when the measurements are actually being carried out until automatic measurements of all the samples are completed. Such a procedure is particularly effective if the samples to be measured are relatively stable chemically and do not require any chemical pretreatment.
In general, most samples suitable for infrared spectrometry satisfy these conditions, and automatic measurements are frequently carried out by using an automatic sample changer. FIG. 4 shows schematically a prior art Fourier transform infrared spectrometer which may be roughly described as comprising a main body 10 including a sample chamber 13 and an automatic sample changer 20 which is detachably attached to this sample chamber 13. Infrared light emitted from a source 11 inside the main body 10 is introduced to an interferometer (the "optical means") 12. The interferometer 12 includes a beam splitter 121, a fixed mirror 122 and a longitudinally slidable mobile mirror 123. The reflected beams from the fixed mirror 122 and the mobile mirror 123 are lead by the beam splitter 121 to propagate in a same direction, resulting in a coherent infrared light beam with amplitude which varies time-wise. This coherent infrared light beam is lead into the sample chamber 13 and directed to one of the sample cells 22 on the automatic sample changer 20. The gas, liquid or solid sample inside the sample cell 22 absorbs the light with characteristic wavelengths, depending on its constituents. The light which passes through the sample cell 22 is lead out of the sample chamber 13 and detected by a detector 14. What is outputted from the detector 14 is an intensity signal as a function of time, and this is Fourier-transformed to obtain a relationship between the frequency (or wavelength of light) and the signal intensity. Thus, the signal outputted from the detector 14 is Fourier-transformed by a signal processor 15 which serves to generate an absorption spectrum. If necessary, this absorption spectrum may be used to calculate the spectral absorptivity and transmissivity.
FIG. 5 shows an example of automatic sample changer 20 having a plurality of sample cells 22 arranged in a circle along the outer periphery of a circular rotary disk 21. The central shaft of this disk 21 is driven directly or indirectly (such as through a suitable decelerating mechanism) by a motor 23 to be rotated. Control signals MC to the motor 23 for selecting a sample cell 22 is provided from a control unit 30 through connectors 24a and 24b.
In general, automatic sample changers of different kinds are provided such as those for carrying different numbers of sample cells, depending, for example, on the sizes of the samples and those having a selected reference sample already set in one part such that a most suitable automatic sample changer can be selected and set inside the sample chamber 13 according to the purpose of and the target for the measurement. If the number of sample cells is different, for example, the angular separation .theta. between mutually adjacent sample cells 22 will also be different and hence the control unit 30 is required to control the motion of the motor 23 differently to select a sample cell, depending on the kind of automatic sample changer which has been set.
With a prior art device of this type, therefore, the user had to input through an input device 16 (such as a keyboard) the distribution of the sample cells (such as their angular separations .theta. and their number) or the position of the reference sample, depending on the type of the installed automatic sample changer. Such an input work is a troublesome procedure and since the user seldom remembers the method of such operations, the user is compelled to make the input by consulting a document such as an instruction book. In summary, such a prior art device was not efficient.
In view of the above, it has been proposed to provide the control unit 30 with the function of identifying the kind of automatic sample changer which has been installed. This may be accomplished, for example, by providing each automatic sample changer 20 with a connector having a plurality of pins such that each automatic sample changer has a different connection scheme for the pins. As an automatic sample changer 20 is set inside the sample chamber 13 and a connecter from the control unit 30 is engaged with the connector on the automatic sample changer, the control unit 30 can identify the type of the automatic sample changer 20 from the condition of the connection of each pin.
With this method, however, the number of different kinds of automatic sample changer that can be identified is limited, depending on the number of the pins on the connector. Since the control unit 30 can identify only the kinds of automatic sample changer which have originally been encoded, it cannot identify any automatic sample changer of a novel structure which did not exist when the encoder was prepared. In other words, extendability of use is very poor with such a scheme.